Bertino's case is not isolated, but the frequency of in-flight medical emergencies is unknown. The Federal Aviation Administration notes there is no method of monitoring how often they happen, because the airlines are not required to report them.

“They're not reported to anyone. They're completely kept in house in each airline,” said Dr. Melissa Mattison, a Boston physician.

The government last looked at the issue in 1993, estimating three medical emergencies a day. A private company called Med-Aire said it tracked nearly 23,000 medical emergencies aboard U.S. flights last year, which is 61 emergencies per day.

Mattison said the information should be tracked, so airlines could be pressured to provide consistent medical supplies on-board.

“As a responder in a medical emergency, it can be very confusing to find the supplies that you need to care for the patient,” Mattison said.

Mattison said medical reporting could provide the data to establish consistent medical kits on all flights.

Until then, the care passengers receive on-board may depend on who else is on the flight.